Piezoelectric device, liquid ejecting head, liquid ejecting apparatus, and method of manufacturing piezoelectric device

ABSTRACT

A piezoelectric device includes a substrate, a diaphragm; and a piezoelectric actuator, in which the substrate, the diaphragm, and the piezoelectric actuator are laminated in this order in a first direction, the diaphragm includes a first layer containing silicon as a constituent element, a third layer disposed between the first layer and the piezoelectric actuator and containing zirconium as a constituent element, and a second layer disposed between the first layer and the third layer and containing at least one impurity element selected from the group consisting of a metal, a metalloid, and a semiconductor other than silicon and zirconium, as a constituent element, and the impurity element diffuses into the third layer.

The present application is based on, and claims priority from JP Application Serial Number 2021-081455, filed May 13, 2021, the disclosure of which is hereby incorporated by reference herein in its entirety.

BACKGROUND 1. Technical Field

The present disclosure relates to a piezoelectric device having a diaphragm and a piezoelectric actuator provided on a substrate, a liquid ejecting head for ejecting a liquid, a liquid ejecting apparatus, and a method of manufacturing the piezoelectric device.

2. Related Art

An ink jet recording head is known as a liquid ejecting head, which is one of the electronic devices. The ink jet recording head includes a substrate provided with a pressure chamber communicating with a nozzle, a diaphragm provided on one surface side of the substrate, and a piezoelectric actuator provided on the diaphragm, and causes a pressure change in the ink in the pressure chamber by driving the piezoelectric actuator, and ejects ink droplets from the nozzle. For example, JP-A-2008-78407 discloses a diaphragm having an elastic film made of silicon dioxide and an insulator film made of zirconium oxide. Here, the elastic film is formed by thermally oxidizing one surface of the silicon single crystal substrate. The insulator film is formed by thermally oxidizing a layer of zirconium alone formed on the elastic film by a sputtering method or the like.

Since the internal stress of the insulator film is tensile stress, there is a problem that the insulator film is destroyed when an external force due to deformation of the piezoelectric actuator is applied.

SUMMARY

According to an aspect of the present disclosure, there is provided a piezoelectric device including a substrate, a diaphragm, and a piezoelectric actuator, in which the substrate, the diaphragm, and the piezoelectric actuator are laminated in this order in a first direction, the diaphragm includes a first layer containing silicon as a constituent element, a third layer disposed between the first layer and the piezoelectric actuator and containing zirconium as a constituent element, and a second layer disposed between the first layer and the third layer and containing at least one impurity element selected from the group consisting of a metal, a metalloid, and a semiconductor other than silicon and zirconium, as a constituent element, and the impurity element diffuses into the third layer.

In addition, according to another aspect of the present embodiment, there is provided a liquid ejecting head including a piezoelectric actuator, a diaphragm that vibrates by driving the piezoelectric actuator, and a flow path formation substrate provided with a pressure chamber that applies pressure to a liquid by a vibration of the diaphragm, in which the flow path formation substrate, the diaphragm, and the piezoelectric actuator are laminated in this order in a first direction, the diaphragm includes a first layer containing silicon as a constituent element, a third layer disposed between the first layer and the piezoelectric actuator and containing zirconium as a constituent element, and a second layer disposed between the first layer and the third layer and containing at least one impurity element selected from the group consisting of a metal, a metalloid, and a semiconductor other than silicon and zirconium, as a constituent element, and the impurity element diffuses into the third layer.

Furthermore, according to still another aspect of the present disclosure, there is provided a liquid ejecting apparatus including the liquid ejecting head according to the above aspect.

Furthermore, according to still another aspect of the present embodiment, there is provided a method of manufacturing a piezoelectric device including a substrate, a diaphragm, and a piezoelectric actuator, in which the substrate, the diaphragm, and the piezoelectric actuator are laminated in this order in a first direction, the diaphragm includes a first layer containing silicon as a constituent element, a third layer disposed between the first layer and the piezoelectric actuator and containing zirconium oxide as a constituent element, a second layer disposed between the first layer and the third layer and containing at least one impurity element selected from the group consisting of a metal, a metalloid, and a semiconductor other than silicon and zirconium, as a constituent element, and the impurity element diffuses into the third layer, the method including forming the first layer on the substrate, forming an impurity element layer containing the impurity element on the first layer, forming a zirconium layer containing zirconium on the impurity element layer, and forming the second layer containing an oxide of the impurity element and the third layer containing zirconium oxide in which the impurity element is diffused by heating the impurity element layer and the zirconium layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an ink jet recording device according to Embodiment 1.

FIG. 2 is an exploded perspective view of a recording head according to Embodiment 1.

FIG. 3 is a plan view of a flow path formation substrate for the recording head according to Embodiment 1.

FIG. 4 is a cross-sectional view of the recording head according to Embodiment 1.

FIG. 5 is a cross-sectional view of the recording head according to Embodiment 1.

FIG. 6 is a flow chart describing a method of manufacturing a piezoelectric device according to Embodiment 1.

FIG. 7 is a cross-sectional view describing a method of manufacturing the piezoelectric device according to Embodiment 1.

FIG. 8 is a cross-sectional view describing a method of manufacturing the piezoelectric device according to Embodiment 1.

FIG. 9 is a cross-sectional view describing a method of manufacturing the piezoelectric device according to Embodiment 1.

FIG. 10 is a cross-sectional view describing a method of manufacturing the piezoelectric device according to Embodiment 1.

FIG. 11 is a graph illustrating an analysis result of Samples 1 and 2 by SIMS.

FIG. 12 is a graph illustrating an analysis result of Samples 1 and 3 by SIMS.

FIG. 13 is a graph illustrating a result of leak current.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, the present disclosure will be described in detail based on embodiments. However, the following description illustrates an aspect of the present disclosure, and can be randomly changed within the scope of the present disclosure. Those having the same reference numerals in each figure indicate the same members, and the description thereof is omitted as appropriate. In addition, in each figure, X, Y, and Z represent three spatial axes that are orthogonal to each other. In the present specification, the directions along these axes are the X direction, the Y direction, and the Z direction. The direction where the arrow in each figure points is the positive (+) direction, and a direction opposite to the arrow is the negative (−) direction. In addition, the three X, Y, and Z spatial axes that do not limit the positive direction and the negative direction will be described as the X axis, the Y axis, and the Z axis. In addition, in each of the following embodiments, as an example, the “first direction” is the −Z direction and the “second direction” is the +Z direction. In addition, viewing in the direction along the Z axis is referred to as “plan view”.

Here, typically, the Z axis is a vertical axis, and the +Z direction corresponds to the downward direction in the vertical direction. However, the Z axis may not be a vertical axis. In addition, the X axis, the Y axis, and the Z axis are typically orthogonal to each other, but are not limited thereto, and may intersect at an angle within a range of, for example, 80° or more and 100° or less.

Embodiment 1

FIG. 1 is a diagram schematically illustrating an ink jet recording device 1 which is an example of a liquid ejecting apparatus according to Embodiment 1 of the present disclosure.

As illustrated in FIG. 1 , the ink jet recording device 1 which is an example of a liquid ejecting apparatus is a printing device that ejects and lands ink, which is a type of liquid, as ink droplets on a medium S such as printing paper, and prints an image or the like by arranging dots formed on the medium S. As the medium S, any material such as a resin film or cloth can be used in addition to the recording paper.

In the following, among the three spatial axes of X, Y, and Z, the moving direction (in other words, main scanning direction) of a recording head 2 described later is defined as the X axis, the transport direction of the medium S orthogonal to the main scanning direction is defined as the Y axis, a plane parallel to the nozzle surface on which a nozzle 21 (refer to FIG. 2 ) of the recording head 2 is formed is defined as the XY plane, a nozzle surface, that is, a direction intersecting the XY plane, a direction orthogonal to the XY plane in the present embodiment, is defined as the Z axis, and the ink droplets are ejected in the +Z direction along the Z axis.

The ink jet recording device 1 includes a liquid container 3, a transport mechanism 4 for sending out the medium S, a control unit 5 which is a control portion, a movement mechanism 6, and an ink jet recording head 2 (hereinafter, also simply referred to as a recording head 2).

The liquid container 3 individually stores a plurality of types (for example, a plurality of colors) of ink ejected from the recording head 2. Examples of the liquid container 3 include a cartridge that can be attached to and detached from the ink jet recording device 1, a bag-shaped ink pack made of a flexible film, an ink tank that can be refilled with ink, and the like. In addition, although not particularly illustrated, a plurality of types of inks having different colors and types are stored in the liquid container 3.

Although not particularly illustrated, the control unit 5 includes, for example, a control device such as a central processing unit (CPU) or a field programmable gate array (FPGA) and a storage device such as a semiconductor memory. The control unit 5 comprehensively controls each element of the ink jet recording device 1, that is, the transport mechanism 4, the movement mechanism 6, the recording head 2, and the like by executing a program stored in the storage device by the control device.

The transport mechanism 4 is controlled by the control unit 5 to transport the medium S in the Y direction, and includes, for example, a transport roller 4 a. The transport mechanism 4 for transporting the medium S is not limited to the transport roller 4 a, and may transport the medium S by a belt or a drum.

The movement mechanism 6 is controlled by the control unit 5 to reciprocate the recording head 2 in the +X direction and the −X direction along the X axis.

Specifically, the movement mechanism 6 of the present embodiment includes a transport body 7 and a transport belt 8. The transport body 7 is a substantially box-shaped structure for accommodating the recording head 2, a so-called carriage, and is fixed to the transport belt 8. The transport belt 8 is an endless belt erected along the X axis. The rotation of the transport belt 8 under the control of the control unit 5 causes the recording head 2 to reciprocate together with the transport body 7 in the +X direction and the −X direction along a guide rail (not illustrated). It is also possible to mount the liquid container 3 on the transport body 7 together with the recording head 2.

Under the control of the control unit 5, the recording head 2 ejects the ink supplied from the liquid container 3 onto the medium S in the +Z direction as ink droplets from each of a plurality of nozzles 21. The ink droplets are ejected from the recording head 2 in parallel with the transport of the medium S by the transport mechanism 4 and the reciprocating movement of the recording head 2 by the movement mechanism 6, so that so-called printing, in which an image with ink is formed on the surface of the medium S, is performed. Here, the recording head 2 is an example of a “piezoelectric device”.

FIG. 2 is an exploded perspective view of an ink jet recording head 2 which is an example of the liquid ejecting head of the present embodiment. FIG. 3 is a plan view of the flow path formation substrate 10 of the recording head 2. FIG. 4 is a cross-sectional view of the recording head 2 according to the line IV-IV of FIG. 3 . FIG. 5 is a cross-sectional view taken along the line V-V of FIG. 3 .

As illustrated in the figure, the recording head 2 of the present embodiment includes a flow path formation substrate 10 as an example of the “substrate”. The flow path formation substrate 10 includes a silicon substrate, a glass substrate, an SOI substrate, and various ceramic substrates.

A plurality of pressure chambers 12 are arranged side by side in the +X direction, which is the first direction, on the flow path formation substrate 10. The plurality of pressure chambers 12 are disposed on a straight line along the +X direction so that the positions in the +Y direction are the same. The pressure chambers 12 adjacent to each other in the +X direction are partitioned by a partition wall 11. As a matter of course, the arrangement of the pressure chambers 12 is not particularly limited thereto, and for example, may be a so-called staggered arrangement in which every other pressure chamber 12 is disposed at positions shifted in the +Y direction, in the pressure chambers 12 arranged side by side in the +X direction.

In addition, the pressure chamber 12 of the present embodiment when viewed in the +Z direction may be a so-called oval shape such as a rounded rectangular shape, an elliptical shape, and an egg shape, with both end portions in the longitudinal direction as a semicircle shape based on a rectangular shape, a parallel quadrilateral shape, or an oblong shape, a circular shape, a polygonal shape, or the like. The pressure chamber 12 corresponds to a “recessed portion” provided in the “substrate”.

The communication plate 15 and the nozzle plate 20 are sequentially laminated on the flow path formation substrate 10 on the +Z direction side.

The communication plate 15 is provided with a nozzle communication passage 16 that communicates with the pressure chamber 12 and the nozzle 21.

In addition, the communication plate 15 is provided with a first manifold portion 17 and a second manifold portion 18 that form a part of a manifold 100 which is a common liquid chamber with which the plurality of pressure chambers 12 communicate in common. The first manifold portion 17 is provided so as to penetrate the communication plate 15 in the +Z direction. In addition, the second manifold portion 18 is provided so as to open in the surface on the +Z direction side without penetrating the communication plate 15 in the +Z direction.

Furthermore, the communication plate 15 is provided with a supply communication passage 19 communicating with the end portion of the Y axis of the pressure chamber 12 independently in each of the pressure chambers 12. The supply communication passage 19 communicates with the second manifold portion 18 and the pressure chamber 12 to supply the ink in the manifold 100 to the pressure chamber 12.

As such a communication plate 15, a silicon substrate, a glass substrate, an SOI substrate, various ceramic substrates, a metal substrate such as a stainless steel substrate, or the like can be used. It is preferable that the communication plate 15 uses a material substantially the same as the coefficient of thermal expansion of the flow path formation substrate 10. By using a material having substantially the same coefficient of thermal expansion between the flow path formation substrate 10 and the communication plate 15 in this manner, it is possible to reduce the occurrence of warpage due to heat due to the difference in the coefficient of thermal expansion.

The nozzle plate 20 is provided on the side of the communication plate 15 opposite to the flow path formation substrate 10, that is, on the surface on the +Z direction side.

The nozzle plate 20 is formed with the nozzles 21 that communicate with each of the pressure chambers 12 via the nozzle communication passage 16. In the present embodiment, the plurality of nozzles 21 are provided with two rows of nozzles arranged side by side in a row along the +X direction and separated from each other in the +Y direction. That is, the plurality of nozzles 21 in each row are disposed so that the positions in the +Y direction are the same as each other. As a matter of course, the arrangement of the nozzles 21 is not particularly limited thereto, and for example, may be a so-called staggered arrangement in which every other nozzle 21 is disposed at positions shifted in the +Y direction, in the nozzles 21 arranged side by side in the +X direction. As such a nozzle plate 20, a silicon substrate, a glass substrate, an SOI substrate, various ceramic substrates, a metal substrate such as a stainless steel substrate, an organic substance such as a polyimide resin, or the like can be used. It is preferable to use a material for the nozzle plate 20 that is substantially the same as the coefficient of thermal expansion of the communication plate 15. By using materials having substantially the same coefficient of thermal expansion between the nozzle plate 20 and the communication plate 15 in this manner, it is possible to reduce the occurrence of warpage due to heat due to the difference in the coefficient of thermal expansion.

The diaphragm 50 and the piezoelectric actuator 300 are sequentially laminated on the surface of the flow path formation substrate 10 on the −Z direction side. That is, the flow path formation substrate 10, the diaphragm 50, and the piezoelectric actuator 300 are laminated in this order in the −Z direction.

As illustrated in FIGS. 2 and 4 , a protective substrate 30 having substantially the same size as the flow path formation substrate 10 is bonded to the surface of the flow path formation substrate 10 in the −Z direction. The protective substrate 30 has a holding portion 31 which is a space for protecting the piezoelectric actuator 300. The holding portions 31 are independently provided for each row of the piezoelectric actuators 300 arranged side by side in the +X direction, and are formed in two side by side in the +Y direction. In addition, the protective substrate 30 is provided with a through-hole 32 penetrating in the +Z direction between two holding portions 31 arranged side by side in the +Y direction. The end portions of an individual lead electrode 91 and a common lead electrode 92 drawn from the electrodes of the piezoelectric actuator 300 are extended so as to be exposed in the through-hole 32, and the individual lead electrode 91 and the common lead electrode 92, and the wiring substrate 120 are electrically coupled to one another in the through-hole 32.

In addition, as illustrated in FIG. 4 , a case member 40 for defining the manifold 100 communicating with a plurality of pressure chambers 12 together with the flow path formation substrate 10 is fixed on the protective substrate 30. The case member 40 has substantially the same shape as that of the communication plate 15 described above in plan view, and is bonded to the protective substrate 30 and also to the communication plate 15 described above. In the present embodiment, the case member 40 is bonded to the communication plate 15. In addition, although not particularly illustrated, the case member 40 and the protective substrate 30 are also bonded to each other.

Such a case member 40 has a recessed portion 41 having a depth for accommodating the flow path formation substrate 10 and the protective substrate 30 on the protective substrate 30 side. The recessed portion 41 has a wider opening area than that of the surface on which the protective substrate 30 is bonded to the flow path formation substrate 10. The opening surface of the recessed portion 41 on the nozzle plate 20 side is sealed by the communication plate 15 in a state where the flow path formation substrate 10 and the like are accommodated in the recessed portion 41. As a result, a third manifold portion 42 is defined by the case member 40 and the flow path formation substrate 10 on the outer peripheral portion of the flow path formation substrate 10. The manifold 100 of the present embodiment is configured to include the first manifold portion 17 and the second manifold portion 18 provided in the communication plate 15, and the third manifold portion 42 defined by the case member 40 and the flow path formation substrate 10. The manifold 100 is continuously provided in the +X direction in which the pressure chambers 12 are arranged side by side, and the supply communication passages 19 that communicate each of the pressure chambers 12 and the manifold 100 are arranged side by side in the +X direction. In addition, the case member 40 is provided with an introduction port 44 for communicating ink with the manifold 100 and supplying ink to each manifold 100. In addition, the case member 40 is provided with a coupling port 43 through which the wiring substrate 120 is inserted so as to communicate with the through-hole 32 of the protective substrate 30, which will be described in detail later.

In addition, a compliance substrate 45 is provided on the surface of the communication plate 15 on the +Z direction side where the first manifold portion 17 and the second manifold portion 18 open. The compliance substrate 45 seals the openings of the first manifold portion 17 and the second manifold portion 18 on the liquid ejecting surface 20 a side. In the present embodiment, such a compliance substrate 45 includes a sealing film 46 made of a flexible thin film and a fixed substrate 47 made of a hard material such as metal. Since a region of the fixed substrate 47 facing the manifold 100 is an opening portion 48 completely removed in the thickness direction, one surface of the manifold 100 is a compliance portion 49 which is a flexible portion sealed only by the flexible sealing film 46.

The diaphragm 50 and the piezoelectric actuator 300 of the present embodiment will be described.

As illustrated in FIGS. 4 and 5 , the piezoelectric actuator 300 includes a first electrode 60, a piezoelectric layer 70, and a second electrode 80, which are sequentially laminated from the +Z direction side, which is on the diaphragm 50 side, toward the −Z direction side. The piezoelectric actuator 300 is a pressure generating unit that causes a pressure change in the ink in the pressure chamber 12. Such a piezoelectric actuator 300 is also referred to as a piezoelectric element, and refers to a portion including the first electrode 60, the piezoelectric layer 70, and the second electrode 80. In addition, a portion where piezoelectric strain occurs in the piezoelectric layer 70 when a voltage is applied between the first electrode 60 and the second electrode 80 is referred to as an active portion 310. On the other hand, a portion where piezoelectric strain does not occur in the piezoelectric layer 70 is referred to as an inactive portion. That is, the active portion 310 refers to a portion where the piezoelectric layer 70 is interposed between the first electrode 60 and the second electrode 80. In the present embodiment, the active portion 310 is formed for each pressure chamber 12 which is a recessed portion. That is, a plurality of active portions 310 are formed on the piezoelectric actuator 300. In general, any one of the electrodes of the active portion 310 is configured as an independent individual electrode for each active portion 310, and the other electrode is configured as a common electrode common to the plurality of active portions 310. In the present embodiment, the first electrode 60 constitutes an individual electrode, and the second electrode 80 constitutes a common electrode. As a matter of course, the first electrode 60 may form a common electrode, and the second electrode 80 may form an individual electrode. In the piezoelectric actuator 300, the portion facing the pressure chamber 12 on the Z axis is a flexible portion, and the outer portion of the pressure chamber 12 is a non-flexible portion.

Specifically, as illustrated in FIGS. 3 to 5 , the first electrode 60 constitutes an individual electrode that is separated into each pressure chamber 12 and is independent for each active portion 310. The first electrode 60 is formed to have a width narrower than the width of the pressure chamber 12 in the +X direction. That is, the end portion of the first electrode 60 is located inside the region facing the pressure chamber 12 in the +X direction. In addition, as illustrated in FIG. 4 , the end portion on the nozzle 21 side is disposed outside the pressure chamber 12 in the Y axis of the first electrode 60. An individual lead electrode 91, which is a lead-out wiring, is coupled to an end portion of the first electrode 60 disposed outside the pressure chamber 12 on the Y axis.

As such a first electrode 60, a material having conductivity, for example, iridium (Ir), platinum (Pt), palladium (Pd), gold (Au), nickel (Ni), chromium (Cr), nickel chromium (NiCr), tungsten (W), titanium (Ti), titanium oxide (TIO_(X)), titanium tungsten (TiW), and the like can be used.

As illustrated in FIGS. 3 to 5 , the piezoelectric layer 70 is continuously provided over the +X direction with a predetermined width in the +Y direction. The width of the piezoelectric layer 70 in the +Y direction is longer than the length in the +Y direction, which is the longitudinal direction of the pressure chamber 12. Therefore, the piezoelectric layer 70 extends to the outside of the region facing the pressure chamber 12 on both sides of the pressure chamber 12 in the +Y direction and the −Y direction. The end portion of the piezoelectric layer 70 on the Y axis opposite to the nozzle 21 is located outside the end portion of the first electrode 60. That is, the end portion of the first electrode 60 on the side opposite to the nozzle 21 is covered with the piezoelectric layer 70. In addition, the end portion of the piezoelectric layer 70 on the nozzle 21 side is located inside the end portion of the first electrode 60, and the end portion of the first electrode 60 on the nozzle 21 side is not covered with the piezoelectric layer 70. As described above, the individual lead electrode 91 made of gold (Au) or the like is coupled to the end portion of the first electrode 60 extending to the outside of the piezoelectric layer 70.

In addition, the piezoelectric layer 70 is formed with a recessed portion 71 corresponding to each partition wall 11. The width of the recessed portion 71 in the +X direction is the same as or wider than the width of the partition wall 11. In the present embodiment, the width of the recessed portion 71 in the +X direction is wider than the width of the partition wall 11. As a result, the rigidity of the portion of the pressure chamber 12 of the diaphragm 50 facing both end portions in the +X direction and the −X direction, that is, an arm portion of the diaphragm 50 is suppressed, so that the piezoelectric actuator 300 can be satisfactorily displaced. In addition, the recessed portion 71 may be provided so as to penetrate the piezoelectric layer 70 in the +Z direction, which is the thickness direction, and may be provided halfway in the thickness direction of the piezoelectric layer 70 without penetrating the piezoelectric layer 70 in the +Z direction. That is, the piezoelectric layer 70 may be completely removed from the bottom surface of the recessed portion 71 in the +Z direction, or a part of the piezoelectric layer 70 may remain.

Such a piezoelectric layer 70 is made of a piezoelectric material made of a composite oxide having a perovskite structure represented by the general formula ABO₃. In the present embodiment, lead zirconate titanate (PZT; Pb (Zr, Ti) O₃) is used as the piezoelectric material. By using PZT as the piezoelectric material, the piezoelectric layer 70 having a relatively large piezoelectric constant d31 can be obtained.

In the composite oxide having a perovskite structure represented by the general formula ABO₃, oxygen is 12-coordinated to the A site and oxygen is 6-coordinated to the B site to form an octahedron. In the present embodiment, lead (Pb) is located at the A site, and zirconium (Zr) and titanium (Ti) are located at the B site.

The piezoelectric material is not limited to the above PZT. Other elements may be contained in the A site and the B site. For example, the piezoelectric material may be a perovskite material such as barium zirconate titanate (Ba (Zr, Ti) O₃), lead zirconate titanate lanthanum ((Pb, La) (Zr, Ti) O₃), lead zirconium titanate magnesium niobate (Pb (Zr, Ti) (Mg, Nb) O₃), and lead zirconate titanate niobate (Pb (Zr, Ti, Nb) O₃) containing silicon.

In addition, the piezoelectric material may be a material having a reduced Pb content, a so-called low lead-based material, or a material that does not use Pb, a so-called lead-free material. When a low lead-based material is used as the piezoelectric material, the amount of Pb used can be reduced. In addition, when a lead-free material is used as the piezoelectric material, it is not necessary to use Pb. Therefore, the environmental load can be reduced by using a low lead-based material or a lead-free material as the piezoelectric material.

Examples of the lead-free piezoelectric material include a BFO-based material containing bismuth iron acid (BFO; BiFeO₃). In the BFO, bismuth (Bi) is located at the A site and iron (Fe) is located at the B site. Other elements may be added to BFO. For example, at least one element selected from manganese (Mn), aluminum (Al), lanthanum (La), barium (Ba), titanium (Ti), cobalt (Co), cerium (Ce), samarium (Sm), chromium (Cr), potassium (K), lithium (Li), calcium (Ca), strontium (Sr), vanadium (V), niobium (Nb), tantalum (Ta), molybdenum (Mo), tungsten (W), nickel (Ni), zinc (Zn), praseodymium (Pr), neodymium (Nd), and europium (Eu) may be added to BFO.

In addition, as another example of the lead-free piezoelectric material, there is a KNN-based material containing potassium niobate sodium (KNN; KNaNbO₃). Other elements may be added to KNN. For example, at least one element selected from manganese (Mn), lithium (Li), barium (Ba), calcium (Ca), strontium (Sr), zirconium (Zr), titanium (Ti), bismuth (Bi), tantalum (Ta), antimony (Sb), iron (Fe), cobalt (Co), silver (Ag), magnesium (Mg), zinc (Zn), copper (Cu), vanadium (V), chromium (Cr), molybdenum (Mo), tungsten (W), nickel (Ni), aluminum (Al), silicon (Si), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), and europium (Eu) may be added to KNN.

Piezoelectric materials also include a material having a composition in which a part of the element is missing, a material having a composition in which a part of the element is in excess, and a material having a composition in which a part of the element is replaced with another element. Unless the basic characteristics of the piezoelectric layer 70 change, a material deviating from the composition of stoichiometry due to defects or excess, or a material in which a part of an element is replaced with another element is also included in the piezoelectric material according to the present embodiment. As a matter of course, the piezoelectric material that can be used in the present embodiment is not limited to the material containing Pb, Bi, Na, K, and the like as described above.

As illustrated in FIGS. 2 to 5 , the second electrode 80 is continuously provided on the −Z direction side opposite to the first electrode 60 of the piezoelectric layer 70, and constitutes a common electrode common to the plurality of active portions 310. The second electrode 80 is continuously provided in the +X direction so that the +Y direction has a predetermined width. In addition, the second electrode 80 is also provided on the inner surface of the recessed portion 71, that is, on the side surface of the recessed portion 71 of the piezoelectric layer 70 and on the diaphragm 50 which is the bottom surface of the recessed portion 71. As a matter of course, the second electrode 80 may be provided only on a part of the inner surface of the recessed portion 71, or may not be provided over the entire inner surface of the recessed portion 71. That is, in the present embodiment, on the flow path formation substrate 10, the second electrode 80 is not provided at the end portions of the piezoelectric actuator 300 on the +Y direction side and the −Y direction side and the diaphragm 50 is provided so as to be exposed on the surface in the −Z direction.

As the material of the second electrode 80, precious metal materials such as iridium (Ir), platinum (Pt), palladium (Pd), and gold (Au), and conductive oxides typified by lanthanum nickel oxide (LNO) are used. In addition, the second electrode 80 may be a laminate of a plurality of materials. As the second electrode 80, it is preferable to use one containing iridium (Ir) and titanium (Ti). In the present embodiment, the second electrode 80 uses a laminated electrode of iridium (Ir) and titanium (Ti).

In addition, an individual lead electrode 91, which is a lead-out wiring, is drawn out from the first electrode 60. A common lead electrode 92, which is a lead-out wiring, is drawn out from the second electrode 80. As described above, the flexible wiring substrate 120 is coupled to the end portion of the individual lead electrode 91 and the common lead electrode 92 on the side opposite to the end portion coupled to the piezoelectric actuator 300. The wiring substrate 120 is mounted with a drive circuit 121 having a switching element for driving the piezoelectric actuator 300.

As illustrated in FIG. 5 , the diaphragm 50 includes the first layer 51, the second layer 52, and the third layer 53, which are laminated in the −Z direction in this order. That is, the diaphragm 50 includes the first layer 51, the second layer 52 disposed between the first layer 51 and the piezoelectric actuator 300, and the third layer 53 disposed between the second layer 52 and the piezoelectric actuator 300. The first layer 51 is disposed closest to the diaphragm 50 on the flow path formation substrate 10 side, that is, on the +Z direction side, and is in contact with the surface of the flow path formation substrate 10 on the −Z direction side. In addition, the third layer 53 is disposed closest to the diaphragm 50 on the −Z direction side and is in contact with the piezoelectric actuator 300. The second layer 52 is interposed between the first layer 51 and the third layer 53. In FIGS. 4 and 5 , for convenience of description, the interface between the layers constituting the diaphragm 50 is clearly illustrated, the interface does not required to be clear, and for example, the constituent materials of the two layers may be mixed in the vicinity of the interface between the two layers adjacent to each other. The diaphragm 50 having such a first layer 51, a second layer 52, and a third layer 53 is continuously provided over the entire surface of the flow path formation substrate 10 on the −Z direction side.

The first layer 51 is a layer containing silicon (Si) as a constituent element. Specifically, the first layer 51 is, for example, an elastic film made of silicon oxide (SiO₂). Here, in addition to silicon oxide and the constituent elements, the first layer 51 may contain a small amount of elements such as zirconium (Zr), titanium (Ti), iron (Fe), chromium (Cr) or hafnium (Hf) as impurities. Such impurities have the effect of softening silicon oxide (SiO₂).

As described above, the first layer 51 of the present embodiment contains, for example, silicon oxide. By forming such a first layer 51 by thermally oxidizing a flow path formation substrate 10 made of a silicon single crystal substrate, it is possible to form the first layer 51 with higher productivity than when being formed by a sputtering method.

The silicon in the first layer 51 may exist in the state of an oxide, or may exist in the state of a simple substance, a nitride, an oxynitride, or the like. In addition, the impurities in the first layer 51 may be elements that are inevitably mixed in when the first layer 51 is formed, or may be elements that are intentionally mixed in the first layer 51.

The thickness T1 of the first layer 51 is determined according to the thickness T and the width W of the diaphragm 50. The thickness T1 of the first layer 51 is preferably, for example, in the range of 100 nm or more and 20000 nm or less, and more preferably in the range of 500 nm or more and 1500 nm or less.

The third layer 53 is a layer containing zirconium (Zr) as a constituent element. Specifically, the third layer 53 is, for example, an insulating film made of zirconium oxide (ZrO₂). Here, in addition to zirconium oxide and the constituent elements, the third layer 53 may contain a small amount of elements such as titanium (Ti), iron (Fe), chromium (Cr) or hafnium (Hf) as impurities. In addition, as will be described in detail later, an impurity element which is a constituent element of the second layer 52 is diffused as an impurity in the third layer 53. Such impurities have the effect of softening the zirconium oxide (ZrO₂) and also have the effect of reducing the tensile stress, which is the internal stress of the entire third layer 53.

As described above, the third layer 53 contains, for example, zirconium oxide. For example, such a third layer 53 can be obtained by forming a layer of zirconium alone by a sputtering method or the like, and then thermally oxidizing the layer. Therefore, when forming the third layer 53, the third layer 53 having a desired thickness can be easily obtained. In addition, since zirconium oxide has excellent electrical insulation, mechanical strength, and toughness, the characteristics of the diaphragm 50 can be enhanced by containing zirconium oxide in the third layer 53. In addition, for example, when the piezoelectric layer 70 is made of lead zirconate titanate, the third layer 53 contains zirconium oxide, so that when forming the piezoelectric layer 70, there is also an advantage that it is easy to obtain the piezoelectric layer 70 preferentially oriented to the (100) plane with a high orientation rate.

The zirconium in the third layer 53 may exist in the state of an oxide, or may exist in the state of a simple substance, a nitride, an oxynitride, or the like. In addition, impurities are mixed in the third layer 53. The impurities in the third layer 53 are elements that are inevitably mixed in during the formation of the third layer 53. For example, these inevitably mixed impurities are impurities contained in the zirconium target used when the third layer 53 is formed by the sputtering method. The method of forming the third layer 53 is not limited to the sputtering method, and may be an organic metal chemical vapor deposition method (MOCVD) or the like. In addition, the impurities in the third layer 53 are those in which the impurity elements which are the constituent elements of the second layer 52 are intentionally diffused into the third layer 53. The impurity elements that are the constituent elements of the second layer 52 diffused in the third layer 53 will be described in detail later.

The thickness T3 of the third layer 53 is determined according to the thickness T and the width W of the diaphragm 50. The thickness T3 of the third layer 53 is preferably in the range of, for example, 100 nm or more and 20000 nm or less.

The second layer 52 is a layer that functions as an impurity supply layer for supplying impurities that diffuse into the third layer 53.

Such a second layer 52 is a layer containing at least one selected from the group consisting of a metal, a metalloid, and a semiconductor, unlike silicon which is a constituent element of the first layer 51 and zirconium which is a constituent element of the third layer 53. That is, the constituent element of the second layer 52 is at least one selected from the group consisting of a metal other than silicon and zirconium, a metalloid, or a semiconductor. The constituent elements of the second layer 52 are impurity elements that diffuse into the third layer 53. Such a constituent element of the second layer 52 may exist in the state of an oxide, or may exist in the state of a simple substance. In addition, the second layer 52 may contain only one metal, a metalloid, and a semiconductor, or may contain two or more of these substances. The constituent elements constituting the second layer 52 are diffused into the third layer 53 as impurities, and are also referred to as an “impurity element”.

In addition, the impurity element of the second layer 52 is preferably a transition metal. By using the impurity element of the second layer 52 as the transition metal, the impurity element is easily diffused into the third layer 53 and is easily oxidized.

In addition, the second layer 52 is preferably an oxide of an impurity element. By forming the second layer 52 with an oxide of an impurity element, the adhesion between the second layer 52, the first layer 51, and the third layer 53 can be enhanced as compared with a simple substance, a nitride, or a carbon-based material.

In addition, it is preferable that the impurity element of the second layer 52 is at least one of chromium (Cr) and titanium (Ti). By using at least one of chromium (Cr) and titanium (Ti) as the impurity element in the second layer 52, the impurity element is easily diffused in the third layer 53 and is easily oxidized. In addition, by using at least one of chromium (Cr) and titanium (Ti) as the impurity element of the second layer 52, it is possible to suppress the formation of voids at the interface between the second layer 52 and the third layer 53. Therefore, it is possible to suppress the invasion of moisture into the interface between the second layer 52 and the third layer 53 from the end surface side of the piezoelectric actuator 300. Therefore, it is possible to prevent the zirconium of the third layer 53 from being embrittled by moisture, and to suppress delamination between the third layer 53 and the upper and lower layers of the third layer 53 and damage such as cracks in the third layer 53.

When the second layer 52 contains chromium (Cr), chromium constitutes an oxide, and the second layer 52 contains chromium oxide. Here, the chromium oxide contained in the second layer 52 may be in any state of polycrystalline, amorphous, or single crystal. However, when the chromium oxide contained in the second layer 52 has an amorphous structure in an amorphous state, the compressive stress generated in the second layer 52 can be reduced as compared with the case where the chromium oxide contained in the second layer 52 is in a polycrystalline or single crystal state. As a result, it is possible to reduce the strain generated at the interface between the first layer 51 or the third layer 53 and the second layer 52.

In addition, when the second layer 52 contains titanium (Ti), titanium constitutes an oxide, and the second layer 52 contains titanium oxide.

Titanium oxide is easily transferred by heat. Therefore, when titanium is contained as a constituent element in the second layer 52, the adhesion between the layers of each of the first layer 51 or the third layer 53 and the second layer 52 can be enhanced by the anchor effect or the chemical bond due to the oxide of the constituent element. Moreover, titanium is likely to form an oxide together with silicon or zirconium. Therefore, when titanium is contained as a constituent element in the second layer 52, by forming an oxide together with silicon, titanium can enhance the adhesion between the first layer 51 and the second layer 52, or by forming an oxide together with zirconium, titanium can enhance the adhesion between the second layer 52 and the third layer 53.

Here, the titanium oxide contained in the second layer 52 may be in any state of polycrystalline, amorphous, or single crystal. However, the titanium oxide contained in the second layer 52 is preferably in a polycrystalline or single crystal state, and particularly preferably has a rutile structure as a crystal structure. Among the crystal structures that titanium oxide can take, the rutile structure is the most stable, and even when the rutile structure is moved by heat, the rutile structure does not easily change to polymorphs such as anatase or brookite. Therefore, the thermal stability of the second layer 52 can be enhanced as compared with the case where the crystal structure of titanium oxide contained in the second layer 52 is another crystal structure.

Here, the concentration of the impurity element in the second layer 52 contained in the third layer 53 gradually decreases from the second layer 52 toward the piezoelectric actuator 300 in the −Z direction, which is the first direction. That is, the impurity element is diffused in the −Z direction of the third layer 53, and is distributed at the highest concentration at the interface of the third layer 53 with the second layer 52.

In addition to the impurity elements described above, which are constituent elements, the second layer 52 may contain a small amount of elements such as titanium (Ti), silicon (Si), iron (Fe), chromium (Cr), and hafnium (Hf) as impurities. The impurity of the second layer 52 referred to here is an element different from the impurity element which is a constituent element constituting the second layer 52. For example, the impurity in the second layer 52 is an element contained in the first layer 51 or the third layer 53. For example, the impurities of the second layer 52 exist in an oxide state together with the impurity elements which are the constituent elements of the second layer 52. Even when the diffusion of silicon from the first layer 51 to the second layer 52 is reduced, or even when the silicon diffuses from the first layer 51 to the second layer 52, such impurities in the second layer 52 have the effect of suppressing the diffusion of the silicon into the third layer 53.

In addition, the thickness T2 of the second layer 52 is determined according to the thickness T and the width W of the diaphragm 50, is not particularly limited, and the thickness T2 is preferably thinner than each of the thickness T1 of the first layer 51 and the thickness T3 of the third layer 53. In this case, there is an advantage that the characteristics of the diaphragm 50 can be easily optimized.

Specifically, when the constituent element contained in the second layer 52 is titanium, the thickness T2 of the second layer 52 is preferably in the range of 20 nm or more and 50 nm or less, and more preferably in the range of 25 nm or more and 40 nm or less. In addition, when the constituent element contained in the second layer 52 is chromium, it is preferably in the range of 1 nm or more and 50 nm or less, and more preferably in the range of 2 nm or more and 30 nm or less. From these facts, regardless of whether the constituent element contained in the second layer 52 is titanium or chromium, it can be seen that the preferable conditions are satisfied as long as the thickness T2 of the second layer 52 is contained in the range of 20 nm or more and 50 nm or less. When the thickness T2 is within such a range, the effect of enhancing the adhesion between the first layer 51 and the third layer 53 by the second layer 52 can be suitably exhibited.

On the other hand, when the thickness T2 is too thin, depending on the type of constituent element contained in the second layer 52 and the like, the effect of reducing the diffusion of simple substances of silicon from the first layer 51 by the second layer 52 tends to decrease. For example, when the second layer 52 is made of titanium oxide, when the thickness T2 is too thin, depending on the heat treatment conditions at the time of manufacture, the silicon alone diffused from the first layer 51 to the second layer 52 may reach the third layer 53. On the other hand, when the thickness T2 is too thick, the heat treatment when manufacturing the second layer 52 may not be sufficiently performed, and as a result of the long time required for the thermal oxidation, the other layers may be adversely affected.

By supplying the impurity element of the second layer 52 to the third layer 53 and diffusing the impurity element in this manner, the third layer 53 contains zirconium (Zr) and the constituent elements of the second layer 52 as impurity elements. By diffusing the impurity element of the second layer 52 into the third layer 53 in this manner, the tensile stress, which is the internal stress of the entire third layer 53, can be reduced. That is, the internal stress of the third layer 53 is a tensile stress, but the volume expands due to the impurity element, and the impurity element acts as a compressive stress, so that the tensile stress of the entire third layer 53 is reduced. Therefore, by diffusing the impurity element of the second layer 52 into the third layer 53 and reducing the tensile stress of the entire third layer 53, it is possible to prevent the third layer 53 from being destroyed when an external force is applied to the third layer 53 due to the deformation of the piezoelectric actuator 300. The impurity elements constituting the second layer 52 capable of diffusing into the third layer 53 and reducing the tensile stress of the third layer 53 has the same effect even when the second layer 52 is a metal, a metalloid, or a semiconductor other than the above-described titanium (Ti) and chromium (Cr).

The impurity element which is a constituent element of the second layer 52 may exist in the third layer 53 in the state of an oxide, or may exist in the state of a simple substance, a nitride or an oxynitride. In order to convert the impurity element in the third layer 53 into a nitride or an oxynitride, the nitride or the oxynitride can be formed, for example, by simultaneously heating the second layer 52 and the third layer 53 in a nitrogen gas or a gas containing nitrogen as a constituent atom.

FIG. 6 is a flow chart for describing a method of manufacturing a piezoelectric device. FIGS. 7 to 10 is cross-sectional views for describing a method of manufacturing a piezoelectric device. Hereinafter, the method of manufacturing the piezoelectric device will be described by taking a case of manufacturing a recording head based on FIGS. 6 to 10 as an example.

As illustrated in FIG. 6 , the method of manufacturing the recording head includes a substrate preparation step S10, a diaphragm forming step S20, a piezoelectric actuator forming step S30, and a pressure chamber forming step S40. In addition, the diaphragm forming step S20 includes a first layer forming step S21, an impurity element layer forming step S22, a zirconium layer forming step S23, and a second layer and a third layer forming step S24. Hereinafter, each step will be described in sequence.

The substrate preparation step S10 is a step of preparing a substrate to be a flow path formation substrate 10. The substrate is, for example, a silicon single crystal substrate.

The diaphragm forming step S20 is a step of forming the diaphragm 50 described above, and is performed after the substrate preparation step S10. In the diaphragm forming step S20, the first layer forming step S21, the impurity element layer forming step S22, the zirconium layer forming step S23, and the second layer and the third layer forming step S24 are performed in this order.

As illustrated in FIG. 7 , the first layer forming step S21 is a step of forming the first layer 51 described above. In the first layer forming step S21, for example, one surface of the silicon single crystal substrate prepared in the substrate preparation step S10 is thermally oxidized to form a first layer 51 made of silicon oxide (SiO₂). The method of forming the first layer 51 is not particularly limited thereto, and may be formed by, for example, a sputtering method, a chemical vapor deposition method (CVD method), a vacuum vapor deposition method (PVD method), an atomic layer deposition method (ALD method), a spin coating method, or the like.

As illustrated in FIG. 8 , the impurity element layer forming step S22 is a step of forming an impurity element layer which is a constituent element of the second layer 52, that is, an impurity element layer 152. In the impurity element layer forming step S22, for example, the impurity element layer 152, which is a layer of impurity element, is formed on the first layer 51 by a sputtering method. The formation of the impurity element layer 152 is not particularly limited thereto, and for example, a CVD method, a PVD method, an ALD method, a spin coating method, or the like may be used.

As illustrated in FIG. 9 , the zirconium layer forming step S23 is a step of forming a zirconium layer which is a constituent element of the third layer 53, that is, a zirconium layer 153. In the zirconium layer forming step S23, for example, the zirconium layer 153, which is a layer of zirconium, is formed on the impurity element layer 152 by a sputtering method. The formation of the zirconium layer 153 is not particularly limited thereto, and for example, a CVD method, a PVD method, an ALD method, a spin coating method, or the like may be used.

As illustrated in FIG. 10 , the second layer and the third layer forming step S24 is a step of simultaneously forming the second layer 52 and the third layer 53 from the impurity element layer 152 and the zirconium layer 153. In the second layer and third layer forming step S24, by simultaneously heating the impurity element layer 152 and the zirconium layer 153, the impurity element layer 152 is thermally oxidized to form the second layer 52 which is an oxide of an impurity element, and the zirconium layer 153 is thermally oxidized to form the third layer 53 which is zirconium oxide. By simultaneously thermally oxidizing the impurity element layer 152 and the zirconium layer 153 to form the second layer 52 and the third layer 53, the impurity elements that are the constituent elements of the impurity element layer 152 can be diffused into the third layer 53. In addition, by simultaneously heating the impurity element layer 152 and the zirconium layer 153 to form the second layer 52 and the third layer 53, the concentration of the impurity element in the second layer 52 contained in the third layer 53 gradually decreases from the second layer 52 toward the piezoelectric actuator 300 in the −Z direction, which is the first direction. That is, the impurity element is diffused in the −Z direction of the third layer 53, and is distributed at the highest concentration at the interface of the third layer 53 with the second layer 52. By increasing the concentration of the impurity element at the interface on the second layer 52 side of the third layer 53, the tensile stress of the internal stress can be significantly reduced at the interface on the second layer 52 side of the third layer 53. Therefore, it is possible to greatly reduce the tensile stress at the interface on the second layer 52 side, where cracks are most likely to occur in the third layer 53, and suppress the occurrence of cracks in the third layer 53.

The piezoelectric actuator forming step S30 is a step of forming the piezoelectric actuator 300 described above, and is performed after the second layer and the third layer forming step S24. In the piezoelectric actuator forming step S30, the first electrode 60, the piezoelectric layer 70, and the second electrode 80 are formed on the third layer 53 in this order.

Each of the first electrode 60 and the second electrode 80 is formed by, for example, a known film forming technique such as a sputtering method, and a known processing technique using a photolithography method and etching. For the piezoelectric layer 70, for example, a precursor layer of the piezoelectric layer 70 is formed by a sol-gel method, and the precursor layer is fired and crystallized to form the piezoelectric layer 70. As a matter of course, the method of forming the piezoelectric layer 70 is not particularly limited thereto, and for example, the piezoelectric layer 70 may be formed by a metal-organic decomposition (MOD) method, a sputtering method, a laser ablation method, or the like. The piezoelectric layer 70 is formed into a predetermined shape by a known processing technique using a photolithography method, etching, or the like.

After the piezoelectric actuator 300 is formed, if necessary, a surface of both sides of the substrate after the formation, which is different from the surface on which the piezoelectric actuator 300 is formed, is ground by chemical mechanical polishing (CMP) or the like to flatten the surface or to adjust the thickness of the substrate.

The pressure chamber forming step S40 is a step of forming the pressure chamber 12 described above, and is performed after the piezoelectric actuator forming step S30. In the pressure chamber forming step S40, for example, the pressure chamber 12 is formed by anisotropic etching on a surface of both sides of the silicon single crystal substrate after the formation of the piezoelectric actuator 300, which is different from the surface on which the piezoelectric actuator 300 is formed. As a result, the flow path formation substrate 10 in which the pressure chamber 12 is formed is obtained. At this time, for example, a potassium hydroxide aqueous solution (KOH) or the like is used as the etching solution for anisotropic etching on the silicon single crystal substrate. In addition, at this time, the first layer 51 functions as a stop layer for stopping the anisotropic etching.

After the pressure chamber forming step S40, the recording head 2 is manufactured by appropriately performing a step of bonding the protective substrate 30, the communication plate 15, and the like to the flow path formation substrate 10 with an adhesive.

Sample 1

By thermally oxidizing one surface of an 8-inch silicon wafer, a first layer 51 having a thickness of 1400 nm made of silicon oxide was formed.

Next, a film made of zirconium was formed on the first layer 51 by a sputtering method, and the film was thermally oxidized at approximately 900° C. to form a third layer 53 having a thickness of 394 nm made of zirconium oxide.

As described above, a diaphragm 50 made of the first layer 51 and the third layer 53 was prepared.

Sample 2

An impurity element layer 152 made of titanium was formed on the same first layer 51 as Sample 1 described above by a sputtering method.

Next, a zirconium layer 153 made of zirconium was formed on the impurity element layer 152 by a sputtering method.

Next, by simultaneously thermally oxidizing the impurity element layer 152 and the zirconium layer 153 at approximately 900° C., a second layer 52 having a thickness of 10 nm made of titanium oxide and a third layer 53 having a thickness of 394 nm made of zirconium oxide were formed.

As described above, a diaphragm 50 made of the first layer 51, the second layer 52, and the third layer 53 was prepared.

Sample 3

An impurity element layer 152 made of chromium was formed on the same first layer 51 as Sample 1 described above by a sputtering method.

Next, a zirconium layer 153 made of zirconium was formed on the impurity element layer 152 by a sputtering method.

Next, by simultaneously thermally oxidizing the impurity element layer 152 and the zirconium layer 153 at approximately 900° C., a second layer 52 having a thickness of 10 nm made of titanium oxide and a third layer 53 having a thickness of 394 nm made of zirconium oxide were formed.

As described above, a diaphragm 50 made of the first layer 51, the second layer 52, and the third layer 53 was prepared.

Test Example 1

Samples 1 to 3 were exposed to a water vapor content atmosphere of heavy water having a temperature of 45° C. and a humidity of 95% RH or more for 24 hours, and analyzed by secondary ion mass spectrometry (SIMS). The results at this time are illustrated in FIGS. 11 and 12 and Table 1 below. In addition, the amount of warpage of the silicon wafers of Samples 1 to 3 was measured. The results are illustrated in Table 1 below together with the results of Test Example 1.

TABLE 1 Number of impurity Amount of atoms in third layer warpage of wafer (average) [cps] [μm] Stress Sample 1 1 to 10 59.9 Tensile Sample 2 30 to 1000000 43.3 Weak tensile than sample 1 Sample 3 40 to 1000000 39.8 Weak tensile than sample 1

As illustrated in Table 1 and FIGS. 11 and 12 , since the number of impurity atoms in the third layer 53 is detected within one digit from the measurement limit value (0.4), impurity elements of the second layer 52 are not diffused in the third layer 53.

On the other hand, as illustrated in Tables 1, and FIGS. 11 and 12 , in Samples 2 and 3, the constituent elements of the second layer 52 are diffused as impurities in the third layer 53. That is, the impurity element which is a constituent element of the second layer 52 is diffused in the thickness direction of the third layer 53. In addition, the concentration of the impurity element of the second layer 52 contained in the third layer 53 gradually decreases as the distance from the second layer 52 increases in the thickness direction.

In addition, as illustrated in Table 1, in sample 1, the amount of warpage of the silicon wafer is large and the internal stress of the entire diaphragm 50 is tensile stress, whereas the amount of warpage of the silicon wafers of Samples 2 and 3 is smaller than that of Sample 1. Therefore, the diaphragm 50 of Samples 2 and 3 has a reduced tensile stress, which is an internal stress, as compared with the diaphragm 50 of Sample 1.

In addition, it is preferable that the valences of the second layer 52 and the third layer 53 are the same as each other. Here, the fact that the valences of the second layer 52 and the third layer 53 are the same as each other means that the difference X between the valences of the main constituent elements of the second layer 52 and the valences of the main constituent elements of the third layer 53 is within the range of −0.5≤X<+0.5. By making the valences of the second layer 52 and the third layer 53 the same as each other in this manner, since the insulating property of the entire diaphragm 50 is improved, it is possible to suppress a leak current between a plurality of active portions 310 of the piezoelectric actuator 300. Therefore, it is possible to suppress the leak current and reduce the decrease in displacement of the active portion 310 due to the leak current.

For example, when the third layer 53 is made of the +4 valences of zirconium oxide (ZrO₂), as the constituent elements of the second layer 52, it is preferable to use titanium, hafnium, iridium, and the like, which have the same +4 valences and are stable.

In addition, it is preferable that the valences between the second layer 52 and the third layer 53 are different from each other. Here, the fact that the valences between the second layer 52 and the third layer 53 are different from each other means that the difference X between the valences of the main constituent elements of the second layer 52 and the valences of the main constituent elements of the third layer 53 is within the range of X<−0.5, +0.5≤X. That is, when the constituent element of the second layer 52 has +4 valences, the constituent element of the third layer 53 has preferably smaller than +3.5 valences or +4.5 valences or more.

As described above, by making the valences of the second layer 52 and the third layer 53 different from each other, the constituent elements of the second layer 52 can easily move to the third layer 53 on the −Z direction side. Therefore, when the active portion 310 is selectively driven, by generating a leak current in the other active portion 310 that is not driven and passing a minute current, it is possible to suppress deterioration variation between the active portion 310 that is continued to move and the other active portion 310 that does not move. Therefore, it is possible to suppress variations in the decrease in displacement of the plurality of active portions 310, suppress variations in the ejection characteristics of ink droplets, and improve the print quality.

For example, when the third layer 53 is made of the +4 valences of zirconium oxide (ZrO₂), as the constituent element of the second layer 52, it is preferable to use chromium, aluminum, tantalum or the like having a valence different from that of the third layer 53.

Sample 4

By thermally oxidizing one surface of the silicon single crystal substrate having the plane orientation (110), the first layer 51 having a thickness of 1400 nm made of silicon oxide was formed.

Next, a film made of zirconium was formed on the first layer 51 by a sputtering method, and the film was thermally oxidized at 900° C. to form a third layer 53 having a thickness of 400 nm made of zirconium oxide. As a result, the diaphragm 50 including the first layer 51 and the third layer 53 was formed.

Next, the first electrode 60, the piezoelectric layer 70, and the second electrode 80 were formed and patterned on the diaphragm 50 to form a piezoelectric actuator 300 having the same shape as that of Embodiment 1.

Thereafter, the other surface of the silicon single crystal substrate was anisotropically etched using a potassium hydroxide aqueous solution (KOH) or the like as an etching solution to form a recessed portion having the first layer 51 as the bottom surface.

Sample 5

The third layer 53 was the same as that of Sample 4 except that the thickness was set to 645 nm.

Sample 6

An impurity element layer 152 made of titanium was formed on the first layer 51 of Sample 4 by a sputtering method.

Next, a zirconium layer 153 made of zirconium was formed on the impurity element layer 152 by a sputtering method.

Next, by simultaneously thermally oxidizing the impurity element layer 152 and the zirconium layer 153 at approximately 900° C., a second layer 52 having a thickness of 40 nm made of titanium oxide and a third layer 53 having a thickness of 250 nm made of zirconium oxide were formed.

The same piezoelectric actuator 300 as Sample 4 was formed on the diaphragm 50, and a recessed portion was formed.

Sample 7

An impurity element layer 152 made of chromium was formed on the first layer 51 of Sample 4 by a sputtering method.

Next, a zirconium layer 153 made of zirconium was formed on the impurity element layer 152 by a sputtering method.

Next, by simultaneously thermally oxidizing the impurity element layer 152 and the zirconium layer 153 at approximately 900° C., a second layer 52 having a thickness of 40 nm made of chromium oxide and a third layer 53 having a thickness of 500 nm made of zirconium oxide were formed.

The same piezoelectric actuator 300 as Sample 4 was formed on the diaphragm 50, and a recessed portion was formed.

Sample 8

The third layer 53 was the same as that of Sample 7 described above except that the thickness was set to 250 nm.

Test Example 2

A withstand voltage test described later was performed on a plurality of active portions of each of the piezoelectric actuators of Samples 4 to 8 to obtain an average value. The results are illustrated in FIG. 13 and Table 2 below.

In the withstand voltage test, the voltage applied between the first electrode 60 and the second electrode 80 is changed from 40 V to 180 V, and when the leak current exceeds 1000 nA, the voltage application is stopped. The voltage exceeding 1000 nA is defined as “withstand voltage”.

TABLE 2 Drive other active portion Leak current with slight Film configuration (relative ratio) vibration Sample 4 ZrO₂ (400 nm)/SiO₂ 1 Absent Sample 5 ZrO₂ (645 nm)/SiO₂ Approximately Absent 1.2 Sample 6 ZrO₂ (250 nm)/TiO₂/SiO₂ Approximately Absent 1.5 Sample 7 ZrO₂ (500 nm)/CrO_(x)/SiO₂ 2 to 6 Present Sample 8 ZrO₂ (250 nm)/CrO_(x)/SiO₂ 10 to 100 Present

From the results illustrated in FIG. 13 and Table 2, by aligning the valences of the third layer 53 and the second layer 52 as in Sample 6, the insulating property of the diaphragm 50 is improved, and the leak current between the plurality of active portions 310 can be suppressed.

In addition, by making the valences of the third layer 53 and the second layer 52 different from each other as in Samples 7 and 8, the leak current can be increased to drive the other active portion 310 with a slight vibration.

As described above, the recording head 2, which is an example of the piezoelectric device of the present disclosure, includes the flow path formation substrate 10 which is the substrate, the diaphragm 50, and the piezoelectric actuator 300, and the flow path formation substrate 10, the diaphragm 50, and the piezoelectric actuator 300 are laminated in this order in the −Z direction as the first direction. In addition, the diaphragm 50 includes the first layer 51 containing silicon as a constituent element, and the third layer 53 disposed between the first layer 51 and the piezoelectric actuator 300 and containing zirconium as a constituent element. In addition, the diaphragm 50 includes the second layer 52 disposed between the first layer 51 and the third layer 53, and containing at least one impurity element selected from the group consisting of a metal, a metalloid, and a semiconductor as a constituent element, unlike silicon and zirconium. The impurity element of the second layer 52 diffuses into the third layer.

By diffusing the impurity element, which is a constituent element of the second layer 52, into the third layer 53 in this manner, the tensile stress, which is the internal stress of the entire third layer 53, can be reduced. Therefore, it is possible to prevent the third layer 53 from being destroyed when an external force is applied to the third layer 53 due to the deformation of the piezoelectric actuator 300.

In addition, in the recording head 2 of the present embodiment, the impurity element is preferably a transition metal. As described above, since the second layer 52 contains a metal element of the transition metal as a constituent element, the impurity element is easily diffused into the third layer 53 and is easily oxidized as the second layer 52.

In addition, in the recording head 2 of the present embodiment, the second layer 52 is preferably an oxide of an impurity element. Accordingly, by forming the second layer 52 with an oxide of an impurity element, the adhesion between the second layer 52, the first layer 51, and the third layer 53 can be enhanced as compared with a simple substance, a nitride, or a carbon-based material.

In addition, in the recording head 2 of the present embodiment, the impurity element is preferably at least one selected from the group consisting of titanium, chromium, and aluminum. By using at least one of titanium (Ti), chromium (Cr), and aluminum (Al) as the impurity element of the second layer 52, the impurity element is easily diffused into the third layer 53, and the second layer 52 is easily oxidized. In addition, by using at least one of titanium (Ti), chromium (Cr), and aluminum (Al) as the impurity element of the second layer 52, it is possible to suppress the formation of voids at the interface between the second layer 52 and the third layer 53. Therefore, it is possible to suppress the invasion of moisture into the interface between the second layer 52 and the third layer 53 from the end surface side of the piezoelectric actuator 300. Therefore, it is possible to prevent the zirconium of the third layer 53 from being embrittled by moisture, and to suppress delamination between the third layer 53 and the upper and lower layers of the third layer 53 and damage such as cracks in the third layer 53.

In addition, in the recording head 2 of the present embodiment, it is preferable that the impurity element is at least one of titanium and chromium. By using at least one of titanium (Ti) and chromium (Cr) as the impurity element in the second layer 52, the impurity element is easily diffused into the third layer 53, and the second layer 52 is easily oxidized. In addition, by using at least one of titanium (Ti) and chromium (Cr) as the impurity element of the second layer 52, it is possible to further suppress the formation of voids at the interface between the second layer 52 and the third layer 53. Therefore, it is possible to suppress the invasion of moisture into the interface between the second layer 52 and the third layer 53 from the end surface side of the piezoelectric actuator 300. Therefore, it is possible to prevent the zirconium of the third layer 53 from being embrittled by moisture, and to suppress delamination between the third layer 53 and the upper and lower layers of the third layer 53 and damage such as cracks in the third layer 53.

In addition, in the recording head 2 of the present embodiment, it is preferable that the concentration of the impurity element contained in the third layer 53 may gradually decrease from the second layer 52 toward the piezoelectric actuator 300 in the −Z direction, which is the first direction. By increasing the concentration of the impurity element at the interface between the third layer 53 and the second layer 52, which is particularly fragile, the cracking of the third layer 53 can be suppressed.

In addition, in the recording head 2 of the present embodiment, it is preferable that the second layer 52 and the third layer 53 have different valences from each other. Accordingly, when the active portion 310 is selectively driven, by generating a leak current in the other active portion 310 that is not driven and passing a minute current, it is possible to suppress deterioration variation between the active portion 310 that is continued to move and the other active portion 310 that does not move. Therefore, it is possible to suppress variations in the decrease in displacement of the plurality of active portions 310, suppress variations in the ejection characteristics of ink droplets, and improve the print quality.

In addition, in the recording head 2 of the present embodiment, it is preferable that the second layer 52 and the third layer 53 have the same valence as each other. Accordingly, the insulating property of the diaphragm 50 can be improved, the leak current can be suppressed, and the decrease in displacement of the active portion 310 can be suppressed.

In addition, in the recording head 2 of the present embodiment, it is preferable that the first layer 51 contains silicon oxide and the third layer 53 contains zirconium oxide. Accordingly, the pressure chamber 12 can be formed with high accuracy by etching on the flow path formation substrate 10 by using the first layer 51 as an etching stop layer. In addition, the crystal structure of the piezoelectric layer 70 can be controlled by the surface state of the third layer 53.

In addition, in the recording head 2 of the present embodiment, it is preferable that the second layer 52 contains chromium oxide. As described above, since the second layer 52 contains chromium oxide, the adhesion between the second layer 52 and the third layer 53 can be improved and the formation of voids at the interface can be suppressed.

In addition, in the recording head 2 of the present embodiment, it is preferable that the chromium oxide contained in the second layer 52 has an amorphous structure. Accordingly, the compressive stress which is the internal stress of the second layer 52 can be reduced, and the strain generated at the interface with the first layer 51 or the third layer 53 can be reduced.

In addition, in the recording head 2 of the present embodiment, it is preferable that the second layer 52 contains titanium oxide. As described above, since the second layer 52 contains titanium oxide, the adhesion between the second layer 52 and the third layer 53 can be improved and the formation of voids at the interface can be suppressed.

In addition, in the recording head 2 of the present embodiment, it is preferable that the titanium oxide contained in the second layer 52 has a rutile structure. As described above, since the titanium oxide contained in the second layer 52 has a rutile structure, the thermal stability of the second layer 52 can be improved as compared with the case where the crystal structure of titanium oxide contained in the second layer 52 has another crystal structure.

In addition, the ink jet recording device 1 which is an example of the liquid ejecting apparatus of the present disclosure includes the recording head 2 described above. It is possible to realize the ink jet recording device 1 having improved reliability by suppressing the destruction of the diaphragm 50.

In addition, the recording head 2, which is an example of the piezoelectric device of the present disclosure, includes the flow path formation substrate 10 which is a substrate, the diaphragm 50, and the piezoelectric actuator 300, and the flow path formation substrate 10, the diaphragm 50, and the piezoelectric actuator 300 are laminated in this order in the −Z direction as the first direction. In addition, the diaphragm 50 includes the first layer 51 containing silicon as a constituent element, and the third layer 53 disposed between the first layer 51 and the piezoelectric actuator 300 and containing zirconium as a constituent element. In addition, the diaphragm 50 includes the second layer 52 disposed between the first layer 51 and the third layer 53, and containing at least one impurity element selected from the group consisting of a metal, a metalloid, and a semiconductor as a constituent element, unlike silicon and zirconium. The impurity element of the second layer 52 diffuses into the third layer. Such a method of manufacturing the recording head 2 has a step of forming the first layer 51 on the flow path formation substrate 10. In addition, it has a step of forming the impurity element layer 152 containing an impurity element on the first layer 51. In addition, it has a step of forming the zirconium layer 153 containing zirconium on the impurity element layer 152. In addition, by heating the impurity element layer 152 and the zirconium layer 153, it has a step of forming the second layer 52 containing the oxide of the impurity element and the third layer 53 containing the zirconium oxide in which the impurity element is diffused. By simultaneously heating the impurity element layer 152 and the zirconium layer 153 to simultaneously form the second layer 52 and the third layer 53, the constituent elements of the second layer 52 can be diffused into the third layer 53 as impurity elements.

Other Embodiments

Although each embodiment of the present disclosure has been described above, the basic configuration of the present disclosure is not limited to the above embodiment.

For example, in each of the embodiments described above, the first electrode 60 is an individual electrode of the piezoelectric actuator 300, and the second electrode 80 is a common electrode of the plurality of piezoelectric actuators 300, and the present disclosure is not particularly limited thereto. The first electrode 60 may be a common electrode of the plurality of piezoelectric actuators 300, and the second electrode 80 may be an individual electrode of each piezoelectric actuator 300.

In addition, in the ink jet recording device 1 described above, an example is described in which the recording head 2 is mounted on the transport body 7 and reciprocates along the X axis, which is the main scanning direction, and the present disclosure is not particularly limited thereto. For example, the present disclosure can also be applied to a so-called line-type recording device in which a recording head 2 is fixed and printing is performed by simply moving a medium S such as paper along the Y axis, which is the sub-scanning direction.

In the above embodiment, the ink jet recording head is described as an example of a liquid ejecting head, and the ink jet recording device is described as an example of a liquid ejecting apparatus. The present disclosure is broadly intended for the liquid ejecting head and the liquid ejecting apparatus in general, and can of course be applied to a liquid ejecting head and a liquid ejecting apparatus that eject liquids other than ink. Examples of other liquid ejecting heads include various recording heads used in an image recording device such as a printer, a color material ejecting head used in the manufacture of a color filter such as a liquid crystal display, an electrode material ejecting head used for electrode formation such as an organic EL display and field emission display (FED), a bioorganic substance ejecting head used in biochip manufacturing, and the like. The present disclosure can also be applied to a liquid ejecting apparatus provided with such a liquid ejecting head.

In addition, the present disclosure is not limited to the liquid ejecting head represented by the ink jet recording head, and can be applied to a piezoelectric device such as an ultrasonic device, a motor, a pressure sensor, a pyroelectric element, and a ferroelectric element. In addition, a finished body using these piezoelectric devices, for example, a liquid ejecting apparatus using a liquid ejecting head, an ultrasonic sensor using an ultrasonic device, a robot using a motor as a drive source, an IR sensor using the above pyroelectric element, a ferroelectric memory using a ferroelectric element, and the like are also included in the piezoelectric device. 

What is claimed is:
 1. A piezoelectric device comprising: a substrate; a diaphragm; and a piezoelectric actuator, wherein the substrate, the diaphragm, and the piezoelectric actuator are laminated in this order in a first direction, the diaphragm includes a first layer containing silicon as a constituent element, a third layer disposed between the first layer and the piezoelectric actuator and containing zirconium as a constituent element, and a second layer disposed between the first layer and the third layer and containing at least one impurity element selected from the group consisting of a metal, a metalloid, and a semiconductor other than silicon and zirconium, as a constituent element, and the impurity element diffuses into the third layer.
 2. The piezoelectric device according to claim 1, wherein the impurity element is a transition metal.
 3. The piezoelectric device according to claim 1, wherein the second layer is an oxide of the impurity element.
 4. The piezoelectric device according to claim 1, wherein the impurity element is at least one selected from the group consisting of titanium, chromium, and aluminum.
 5. The piezoelectric device according to claim 4, wherein the impurity element is at least one of titanium and chromium.
 6. The piezoelectric device according to claim 1, wherein a concentration of the impurity element contained in the third layer gradually decreases from the second layer toward the piezoelectric actuator in the first direction.
 7. The piezoelectric device according to claim 1, wherein the second layer and the third layer have different valences.
 8. The piezoelectric device according to claim 1, wherein the second layer and the third layer have the same valence.
 9. The piezoelectric device according to claim 1, wherein the first layer contains silicon oxide, and the third layer contains zirconium oxide.
 10. The piezoelectric device according to claim 1, wherein the second layer contains chromium oxide.
 11. The piezoelectric device according to claim 10, wherein the chromium oxide contained in the second layer has an amorphous structure.
 12. The piezoelectric device according to claim 1, wherein the second layer contains titanium oxide.
 13. The piezoelectric device according to claim 12, wherein the titanium oxide contained in the second layer has a rutile structure.
 14. A liquid ejecting head comprising: a piezoelectric actuator; a diaphragm that vibrates by driving the piezoelectric actuator; and a flow path formation substrate provided with a pressure chamber that applies pressure to a liquid by a vibration of the diaphragm, wherein the flow path formation substrate, the diaphragm, and the piezoelectric actuator are laminated in this order in a first direction, the diaphragm includes a first layer containing silicon as a constituent element, a third layer disposed between the first layer and the piezoelectric actuator and containing zirconium as a constituent element, and a second layer disposed between the first layer and the third layer and containing at least one impurity element selected from the group consisting of a metal, a metalloid, and a semiconductor other than silicon and zirconium, as a constituent element, and the impurity element diffuses into the third layer.
 15. A liquid ejecting apparatus comprising: the liquid ejecting head according to claim
 14. 16. A method of manufacturing a piezoelectric device including a substrate, a diaphragm, and a piezoelectric actuator, in which the substrate, the diaphragm, and the piezoelectric actuator are laminated in this order in a first direction, the diaphragm includes a first layer containing silicon as a constituent element, a third layer disposed between the first layer and the piezoelectric actuator and containing zirconium oxide as a constituent element, and a second layer disposed between the first layer and the third layer and containing at least one impurity element selected from the group consisting of a metal, a metalloid, and a semiconductor other than silicon and zirconium, as a constituent element, and the impurity element diffuses into the third layer, the method comprising: forming the first layer on the substrate; forming an impurity element layer containing the impurity element on the first layer; forming a zirconium layer containing zirconium on the impurity element layer; and forming the second layer containing an oxide of the impurity element and the third layer containing zirconium oxide in which the impurity element is diffused by heating the impurity element layer and the zirconium layer. 